It is well known in the art that certain oily substances, as for example mineral oils, polypropylene oxide and polybutadiene have a defoaming activity. This applies particularly to oily substances of relatively low viscosity. Such oily substances exhibiting defoaming characteristics also include oils of vegetable and animal origin as, for example, rape and rape-seed oil, soy oil and train oils. However, it is well known that the defoaming activity of these known oily substances is insufficient in many instances to cause complete and permanent elimination of foam which is normally formed in and by aqueous solutions or dispersions.
More recently, it has been proposed to use siloxane oils, particularly, methylpolysiloxane oils of low to medium viscosity for the indicated purpose. Reference is thus had to the treatise by W. Noll, "Chemie und Technologie der Silicone", Verlag Chemie GmbH, Weinheim, 1968, pages 540 ff.
It has also been proposed to improve the defoaming activity of defoaming agents by the addition of highly disperse inorganic substances, particularly, highly disperse silica, customarily produced in pyrogenic manner and highly disperse aluminum oxide. Pertinent literature citations in this respect are German Pat. No. 1,067,003 and German Offenlegungsschrift No. 1,914,684.
Further, with a view to improving the distribution of the defoaming substances, emulsifiers have been added to the system. In other instances, preparations were directly produced in the form of emulsions. Examples for such defoaming agents in emulsion form are again German Pat. No. 1,067,003 and German Offenlegungsschrift No. 1,914,684 as referred to above.
The most pronounced improvement of the defoaming effect of defoaming preparations, be they in emulsifiable form or in the form of emulsions proper, has been obtained by the use of methylpolysiloxane oils. However, defoaming preparations on the basis of methylpolysiloxane oils cause serious undesired side effects which in many instances make it impossible to use such systems although they have an excellent defoaming activity. A number of such disadvantages and drawbacks of the known methylpolysiloxane oil containing defoamers is enumerated hereinafter, although the listing is by no means complete.
1. For example, if metal working emulsions are defoamed by such defoaming preparations containing silicone oil, a thin film of silicone oil remains on the treated object. This film negatively affects the further processing of the metal articles. For example, subsequent coating with lacquer or varnish or adhesive uniting of the metal articles is greatly impaired by the presence of this thin silicone oil film. The formation and retention of the oily film is peculiar to silicone oil as distinguished from other oils.
2. If such defoamers are added to printing dyes of aqueous or aqueous-alcoholic basis, the defoaming may be satisfactory but the running of the dyes on the printing rollers during the subsequent printing procedure is negatively affected and printing may be rendered extremely difficult. Similar difficulties occur in rotogravure or copper plate printing and other printing procedures since the wetting capability of the printing paste is considerably reduced by the presence of the silicone containing defoaming preparations.
3. If substrates are defoamed which are subjected to fermentation, the presence of the silicone oil containing defoamers causes frequently a significant growth impediment of the bacteria, yeast and other micro-organisms causing the fermentation.
4. If textile treating agents are defoamed in the indicated manner, the ultimate textile product frequently has spots caused by the silicone oil in the treating agent. These spots usually can not be removed by washing or the like. This phenomenon occurs particularly if the defoaming preparation is used in excess and is pronounced in dyeing procedures since the dye than takes in an uneven manner on the fabric.
5. Due to the abhesive activity of the silicone oils, defoaming of adhesives, seriously reduces the adhesive force of the adhesive preparations.
6. Foam which is produced in paper producing plants, can also successfully be defoamed with silicone oil containing preparations. However, the printability of the ultimate paper is negatively affected. Further, like in the case of textiles, undesired watermark-like spots are formed.
German Pat. Nos. 1,012,602 and 1,040,251 disclose that certain polysiloxane-polyoxyalkylene mixed block polymers can be used as defoaming agents. However, these two patents clearly indicate that but water soluble mixed block polymers are suitable for defoaming purposes and the skilled artisan reading these patents obtains the distinct impression and prejudice that water insoluble block polymers of the indicated kind are unsuitable for defoaming purposes. In these two patents, the portion of the molecular weight which emanates from the oxyethylene groups is equal or larger than the portions which emanate either from the polysiloxane units or the oxypropylene or oxybutylene units. These prior art water soluble mixed block polymers have a lesser defoaming activity than dimethylpolysiloxane oils. (This will be numerically demonstrated hereinafter. See the comparison tests of Example 6 between formulation B and C.)
German Offenlegungsschrift No. 2,123,573 discloses and claims the use of siloxane-oxyalkylene-copolymers in defoaming preparations, the copolymers being soluble in cold water. German Offenlegugungsschrift No. 2,222,998 discloses siloxane-oxyalkylene-copolymers whose polyether block has a ratio of the number of C atoms to the number of O atoms of 2.3 to 2.8. This means that the oxyethylene units constitute at least 20%. Also, these two publications give the distinct impression that the hydrophilic properties are not permitted to fall below a certain minimum value.